JPH1172096A - Pump flow rate controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a necessity of a large capacity memory, enable continuous control, and save energy by rotating a pump at the set number of rotation of the pump which is calculated based on the maximum discharge flow rate and the maximum discharge pressure of the pump in a pipe and the minimum required discharge pressure in the pipe and discharge pressure of the pump in a pressure sensor. SOLUTION: The maximum discharge flow rate and the maximum discharge pressure of a centrifugal pump l in a water supply pipe 6 and the minimum required water supply pressure in the water supply pipe 6 are input in a computing unit 5 in advance. The computing unit 5 calculates the set number of rotation of the pump l based on these values. The set number of rotation is the number of rotation of the centrifugal pump l required to obtain the discharge flow rate given by a resistance curve in the discharge pressure detected by a pressure sensor 2. The resistance curve is a curve of second order which shows the relationship between a water supply amount and water supply pressure in the water supply pipe 6. An inverter 4 and an induction motor 3 are controlled to rotate the centrifugal pump 1 at the set number of rotation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pump flow control device, and more particularly to a pump flow control device which estimates a terminal pressure which is a water pressure at an end of a water supply pipe from a discharge pressure of a pump provided in the water supply pipe. The present invention relates to a pump flow control device capable of controlling a rotation speed. The present invention does not particularly require a memory for storing the performance curves of the pump corresponding to various discharge pressures and discharge flow rates, and can continuously control the pump only by knowing the discharge pressure of the pump. The present invention relates to a pump flow control device.

[0002]

2. Description of the Related Art In recent years, as power electronics control devices have become inexpensive and have improved performance, rotation speed control has been widely used for controlling the amount of water supplied to a pump.

Conventionally, the constant discharge pressure control has been used because the control is simple and the control device is relatively inexpensive. This control method controls the discharge flow rate of the pump by changing the rotation speed of the pump while keeping the discharge pressure constant.

However, in a pipe such as a water supply pipe, when the discharge flow rate of the pump changes, the pipe resistance changes in proportion to the square of the change in the discharge flow rate. Therefore, when the amount of supplied water is small, there is a problem that the terminal pressure of the supplied water pipe becomes too high, and therefore, there is a large loss of energy.

[0005] In recent years, various end pressure constant control devices for maintaining the end pressure in the water supply pipe constant have been proposed.

[0006] Conventionally proposed terminal pressure constant control devices include, for example, a pump, a water supply pipe connected to the pump, and a pressure for measuring a water supply pressure provided near a discharge port of the pump in the water supply pipe. A constant terminal pressure control device including a sensor and a flow rate sensor provided in the water supply pipe and measuring a water supply amount can be given. Here, assuming that the water supply pressure is P and the water supply amount is Q, between P and Q,

[0007]

(Equation 1)

It is known that the relationship of (a: pipe coefficient, b: pressure obtained by adding the required pressure at the end of the water supply pipe to the actual head of the pump) is established. Therefore, in the terminal pressure constant control device, when the water supply amount Q changes, the terminal pressure in the water supply pipe is controlled by controlling the rotation speed of the pump so that the water supply pressure P changes according to the above equation. Control to keep it constant.

[0009] However, in the above-mentioned terminal pressure constant control device, the flow rate sensor used is generally expensive despite its insufficient reliability, and the control of the device itself is complicated. There was also a problem that the device itself became large-scale.

[0010]

Therefore, the terminal pressure of the water supply pipe is estimated from the discharge pressure of the pump, and the rotation speed of the pump is controlled so that the estimated terminal pressure becomes constant.
Various so-called estimated terminal pressure control methods have been proposed.

For example, there has been proposed a method of estimating a pipe resistance from a load condition in a variable speed pump and performing an estimated terminal pressure control based thereon (Japanese Patent No. 2523139).

Further, as another estimated terminal pressure control method, a pump, a variable speed driving means for driving the pump, a control device for controlling the pump, a water supply line connected to the pump, and a water supply line connected to the pump are provided. In a water supply device equipped with a pressure sensor for measuring the pressure in a pipe, a discharge determined by an intersection of a performance curve indicating a relationship between a discharge flow rate and a discharge pressure of a pump at a certain operation speed and a resistance curve of a water supply pipe. Pressure,
There has been proposed a method of controlling a water supply device in which the operation speed of the pump is stored at each of the intersections and controlled by the variable speed drive means so that the operation speed of the pump becomes the stored operation speed (Japanese Patent Publication No. Hei 8-19916). Gazette).

However, in the former control method, since the load due to the pipe resistance is obtained from the value of the current flowing through the motor driving the pump, there is a problem that the error increases. Further, since the load applied to the pump is obtained from the current value flowing through the motor that drives the pump at the same time as the rotation speed of the pump is changed, there is a problem that the control is complicated.

In the latter control method, in order to perform high-precision control, the pressure determined by the intersection of the performance curve and the resistance curve of the water supply line is changed along the resistance curve of the water supply line. However, there is a problem that a large capacity memory is required because a large number of memories must be stored for each operation speed. Then, even if a large-capacity memory is used, even if a large number of the operating speeds and the corresponding pressures are stored, only the rotational speed for each pressure stored in the memory can be output. Performing continuous control was essentially impossible.

[0015] It is an object of the present invention to solve the above-mentioned problems of the conventional estimated terminal pressure control method.

That is, according to the present invention, there is no need to store a large number of pressures determined at the intersection of the performance curve and the resistance curve of the water supply line for each operating speed at the intersection, and continuous control can be easily performed. It is another object of the present invention to provide a pump flow control device that leads to significant energy saving.

[0017]

Means for Solving the Problems A pump flow control device aiming at solving the above problems comprises (1) a pump,
A pressure sensor that measures the discharge pressure of the pump, a motor that drives the pump, a motor control device that controls the number of revolutions of the motor, and a maximum discharge flow rate and a maximum discharge pressure of the pump in the piping, Based on the minimum required discharge pressure, and the discharge pressure of the pump measured by the pressure sensor, calculate the set rotation speed of the pump, and to the motor control device so that the pump rotates at the set rotation speed. And (2) the flow rate control device according to (1), wherein the calculation device comprises: (A) a flow path resistance in a known pipe. Coefficient, minimum required discharge pressure (Po) and maximum discharge flow (Qmax
), The maximum discharge pressure (Pmax) of the pump is obtained, and the maximum flow point (Qmax, Qmax, given by the maximum discharge flow rate (Qmax) and the maximum discharge pressure (Pmax) of the pump is obtained.
Pmax), the maximum number of revolutions (Nmax) corresponding to the performance curve of the pump is determined, and (B) the minimum required discharge pressure (Po) is taken as the shutoff operating pressure, and the shutoff operating pressure (Po) is obtained.
) And the flow rate Q is 0, the shutoff speed (No) of the pump corresponding to the performance curve of the pump passing the shutoff operating point (0, Po) given by (C) (a) A resistance curve f (Q, P) in the pipe given by a quadratic curve connecting the maximum flow point (Qmax, Pmax) and the shutoff operation point (0, Po), and the maximum flow point (Qmax, Pmax). Operating point curve g, which is a locus of similar operating points when the rotation speed of the pump is changed, given by a quadratic curve passing through the pump and the pump stop point (0, 0).
(Q, P) and a performance curve ho (Q, P) of the pump at the shutoff speed (No), a surface surrounded by a closed curve having three sides, and (b) the resistance curve f (Q, P). ), A similar operating point curve g (Q, P), and a surface surrounded by a closed curve having three sides of the performance curve hN (Q, P) of the pump at the set rotation speed (N) are similar. (1) calculating the set rotation speed (N) of the pump in (1) according to a procedure of calculating the set rotation speed (N) at the pressure P measured by the pressure sensor according to claim 1. It is a pump flow control device.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION
As described above, a pump, a pressure sensor for measuring a discharge pressure of the pump, a motor for driving the pump, a motor control device for controlling the number of rotations of the motor, and outputting a control command to the motor control device And a computing device for performing the operation.

The arithmetic unit is configured to calculate the maximum discharge flow rate and the maximum discharge pressure of the pump in the pipe, the minimum required discharge pressure in the pipe, and the discharge pressure of the pump measured by the pressure sensor. A function of calculating a set rotation speed of the pump such that a discharge flow rate at a discharge pressure of the pump is a discharge flow rate given by a resistance curve of the pipe; and the motor control device so that the pump rotates at the set rotation number. Has the function of outputting a control command to the The minimum required discharge pressure is a pressure given by a sum of an actual head in the pipe and a required end pressure, and is a minimum pressure necessary to supply a liquid such as tap water through the pipe. It is. Further, in the arithmetic device, if the discharge flow rate and the discharge pressure of the pump are changed along the resistance curve of the pipe, regardless of the water supply amount,
The above calculation is performed based on the principle that a constant terminal pressure is always obtained.

1. 1 is a schematic diagram showing an example in which a pump flow control device according to the present invention is used in a water supply system.

1.1 Description of Pump Flow Control Apparatus shown in FIG. 1 In the pump flow control apparatus shown in FIG. 1, the centrifugal pump 1 is driven by an induction motor 3. The rotation speed of the induction motor 3 is controlled by inputting an alternating current having a frequency fs by the inverter 4. still,
One end of the rotation shaft of the centrifugal pump 1 is directly connected to one end of the rotation shaft of the induction motor 3. The other end of the rotation shaft of the induction motor 3 is connected to a speed detector 7 that generates pulses of a number corresponding to the rotation speed of the induction motor 3.

A water supply pipe 6 is connected to a discharge port 60 of the centrifugal pump 1. In the vicinity of the outlet of the centrifugal pump 1 in the water supply pipe 6, from the side close to the centrifugal pump 1,
A check valve 61 and an on-off valve 62 are provided. Further, a pressure sensor 2 that measures the discharge pressure of the centrifugal pump 1 and converts the pressure into an electric signal is provided in the water supply pipe 6 near the downstream side outlet of the on-off valve 62.

The discharge pressure measured by the pressure sensor 2 is input to an arithmetic unit 5.

The maximum discharge flow rate and the maximum discharge pressure of the centrifugal pump 1 in the water supply pipe 6 and the minimum required water supply pressure in the water supply pipe 6 are input to the arithmetic unit 5 in advance. Here, the minimum required water supply pressure is the pressure given as the sum of the actual head of the water supply pipe 6 and the required end pressure, and is the minimum pressure required when water is supplied through the water supply pipe 6.

The arithmetic unit 5 calculates the maximum discharge flow rate of the centrifugal pump 1, the maximum discharge pressure, the minimum required water supply pressure,
It has a function of calculating a set rotation speed (N) of the centrifugal pump 1 from the discharge pressure. The resistance curve is a curve indicating the relationship between the amount of water supply and the supply pressure in the water supply pipe 6, and is given by a quadratic curve. The set number of revolutions (N) is the number of revolutions of the centrifugal pump 1 required to obtain the discharge flow rate given by the resistance curve at the discharge pressure detected by the pressure sensor 2. As described above, if the discharge flow rate and the discharge pressure of the centrifugal pump 1 are changed along the resistance curve of the water supply pipe 6 at the end of the water supply pipe 6 regardless of the water supply amount, as described above. It is based on the principle that the required end pressure is always obtained.

Then, the arithmetic unit 5 outputs a control command to the inverter 4 so that the centrifugal pump 1 rotates at the set rotation speed (N). Here, since the centrifugal pump 1 is directly connected to the induction motor 3 as described above,
Is controlled to rotate at the set rotation speed (N), the centrifugal pump 1 also rotates at the set rotation speed (N).

The inverter 4 receives the control command,
The frequency (fs) of the output alternating current is controlled. Speed signal N from speed detector 7 coupled to the rotation axis of induction motor 3
fb is fed back to the inverter 4. The inverter 4 receives the speed signal Nfb from the speed detector 7 and receives a maximum 3% due to the load applied to the induction motor 3 from the centrifugal pump 1.
Compensates for the slip of the induction motor 3
Controls the frequency (fs) of the output alternating current so that the motor rotates at the set speed (N) regardless of the magnitude of the load.

In the pump flow controller of FIG. 1, the centrifugal pump 1 corresponds to a pump in the pump flow controller of the present invention, and the pressure sensor 2 corresponds to a pressure sensor in the pump flow controller of the present invention. The induction motor 3
Corresponds to the motor in the pump flow control device of the present invention,
The inverter 4 and the speed detector 7 correspond to the motor control device in the pump flow control device of the present invention, and the arithmetic device 5
Corresponds to an arithmetic unit in the pump flow control device of the present invention.

1.2 Procedure for Calculating the Set Rotational Speed (N) of the Pump In the calculation device provided in the pump flow control device shown in FIG. 1, the procedure for calculating the set rotational speed (N) of the centrifugal pump 1 will be described. This will be described in detail below.

First, the maximum resistance of the centrifugal pump 1 is determined from the flow resistance coefficient k in the water supply pipe 6, the minimum required water supply pressure (Po) when the pump is stopped, and the maximum discharge flow rate (Qmax) of the centrifugal pump 1. The discharge pressure (Pmax) is determined.

Here, the maximum discharge flow rate (Qmax) in the water supply pipe 6 is the amount of water required when the water taps of the entire building are fully opened in an apartment or office building to be supplied with water by the water supply pipe 6. , The number of hydrants,
It is calculated from the flow rate when one hydrant is fully opened. The flow path resistance coefficient k in the water supply pipe 6 is determined by the arrangement of the pipes and the joints shown in the piping diagram (not shown) in the water supply pipe 6, the inner diameters of these pipes and the joints, and the curvature of the joints. Calculated from radius.

On the other hand, the minimum required discharge pressure in the water supply pipe 6, that is, the minimum required water supply pressure (Po) is, as described above,
The actual head (Ho) in the water supply pipe 6 and the water supply pipe 6
Is the pressure given as the sum with the required end pressure (Hp) at Here, the actual head (Ho) is based on the water supply pipe 6.
At the height from the discharge port of the centrifugal pump 1 to the highest point of the water supply pipe 6.

Maximum discharge pressure of the centrifugal pump 1 (Pmax)
Is given by the sum of the flow path resistance when water flows at the flow rate given by the maximum discharge flow rate (Qmax) and the minimum required feed pressure (Po). Therefore, the maximum discharge pressure (Pmax) is calculated from the maximum discharge flow rate (Qmax), the flow path resistance coefficient k of the pipe 6 and the minimum required water supply pressure (Po) by the formula (I).

[0034]

(Equation 2)

Is obtained.

At this time, the rotation speed of the centrifugal pump 1, that is, the maximum rotation speed (Nmax) is determined by the maximum discharge flow rate (Qmax).
)) And the maximum discharge pressure (Pmax) of the pump, the rotation speed corresponding to the performance curve hmax (Q, P) of the pump passing through the maximum flow point A (Qmax, Pmax).

The minimum required water supply pressure (Po), the maximum discharge flow rate (Qmax), the maximum discharge pressure (Pmax) of the centrifugal pump 1, and the maximum rotation speed (Nmax) thus obtained are determined.
) Is input to the arithmetic unit 5. The arithmetic unit 5 is provided with a numeric keypad or a keyboard, and the above parameters can be input through the numeric keypad or the keyboard.

Next, the minimum required feed water pressure (Po) is defined as the shutoff operating pressure, and the shutoff operating point D (Po,
The rotation speed corresponding to the performance curve of the pump passing through 0) is obtained, and this is set as the cutoff rotation speed (No) of the pump when the pressure is used as the pressure during the shutoff operation of the pump.

The cutoff rotation speed (No) is the maximum rotation speed Nmax.
From the cutoff pressure (Plim) and the minimum required water supply pressure (Po) at

[0040]

(Equation 3)

Therefore,

[0042]

(Equation 4)

Is obtained by

In the arithmetic unit 5, the minimum required feed water pressure (Po), the maximum discharge flow rate (Qmax), the maximum discharge pressure (Pmax) of the centrifugal pump 1, and the maximum rotation speed (Nmax)
), The shutoff speed (No), and the discharge pressure (P) input from the pressure sensor 2, the following equation (II):

[0045]

(Equation 5)

(Where ΔP = Pmax−P and ΔPo
= Pmax-Po. ), The set number of revolutions (N) is calculated.

The procedure for deriving the above formula (II) will be described below.

First, a resistance curve f (Q,
P) is subtracted. The resistance curve f (Q, P) is given by a quadratic curve connecting the maximum flow point A (Qmax, Pmax) and the shutoff operation point D (0, Po). Next, a similar operating point curve g (Q, P) which is a locus of similar operating points when the rotation speed of the pump is changed is drawn. Similar operating point curve g (Q,
P) is given by a quadratic curve passing through the maximum flow point A (Qmax, Pmax) and the pump stop point O (0, 0).

When water is supplied to the water supply pipe 6 using the centrifugal pump 1, the discharge flow rate (Q) and the discharge pressure (P) are
It changes along the resistance curve f (Q, P). Therefore,
A point B (Q, P) corresponding to the discharge pressure (P) can be taken on the resistance curve f (Q, P).

Next, the pump performance curve hmax (Q, P) at the maximum rotation speed (Nmax) and the cutoff rotation speed (No)
) And the pump performance curve hN (Q, P, B) at the point B (Q, P).
P). The performance curve hmax (Q, P) of the pump at the maximum rotation speed (N) max passes through the maximum flow point A (Qmax, Pmax) as described above, and the cutoff rotation speed (No)
)), The performance curve ho (Q, P) of the pump is
As described above, the vehicle passes the cutoff operation point D (0, Po). A point at which the performance curves hN (Q, P) and ho (Q, P) intersect with the similar operating point curve g (Q, P) is referred to as a point C, respectively.
(Q ', P') and point E (Q1, P1). The maximum flow point A (Qmax, Pmax), point B (Q, P), point C
(Q ', P'), deadline operating point D (0, Po), point E (Q
1, P1), the pump stop point O (0, 0), the resistance curve f (Q, P), the similar operating point curve g (Q, P), the performance curve hmax (Q, P), and the performance curve ho. FIG. 2 shows the relationship between (Q, P) and the performance curve hN (Q, P).

It is known that the flow resistance in the water supply pipe 6 is proportional to the amount of water flowing inside the water supply pipe 6, that is, the square of the discharge flow rate (Q).

Then, as is apparent from FIG.
The flow path resistance of the water supply pipe 6 at max is given by Pmax-Po and the water supply pipe 6 at the flow rate Q given at point B
Is given by P-Po,

[0053]

(Equation 6)

The following relationship holds.

When the minimum required water supply pressure is 0, the centrifugal pump discharge pressure (P), discharge flow rate (Q) and rotation speed (N)
Between

[0056]

(Equation 7)

It is generally known that the following relationship holds. Therefore, the maximum discharge flow rate at the maximum flow point A (Qma
x), maximum discharge pressure (Pmax), and maximum rotation speed (Nma
x), discharge flow rate (Q '), discharge pressure (P'), and rotation speed (N) at point C, and discharge flow rate (Q1), discharge pressure (P1), and rotation speed (No) at point E. Between

[0058]

(Equation 8)

[0059]

(Equation 9)

The following relationship is established. Therefore, the maximum discharge pressure (Pmax), the discharge pressure at point C (P '),
Between the discharge pressure (P1) at the point E,

[0061]

(Equation 10)

[0062]

[Equation 11]

The following relationship holds.

The relationship between P 'and Pmax, P, No, and Nmax will now be determined.

As is clear from FIG. 2, the performance curve hma
Since x (Q, P), performance curve hN (Q, P) and performance curve ho (Q, P) are almost parallel, resistance curve f
(Q, P) and similar operating point curve g (Q, P) and performance curve h
o (Q, P), a substantially triangular surface surrounded by a closed curve ADE, an operating point curve g (Q, P) similar to the resistance curve f (Q, P) and hN (Q, P) Can be considered to be similar to each other with the substantially triangular surface surrounded by the closed curved surface ABC formed by. Therefore, between P ′, Pmax, P, Po, and P1,

[0066]

(Equation 12)

The following relationship holds. When this equation (VIII) is solved for P ′, for P ′,

[0068]

(Equation 13)

The following relationship holds.

Here, from the above formula (VI),

[0071]

[Equation 14]

The following relationship can be derived. By substituting the formulas (X) and (VII) into the formula (IX),

[0073]

(Equation 15)

Is derived.

By solving equation (XI) for the set number of revolutions (N), equation (II) is derived.

1.3 Procedure in which the Computing Device 5 Controls the Inverter 4 In the pump flow control device shown in FIG. 1, the computing device 5 operates at the set rotation speed (N) calculated as described above. A control command is output to the inverter 4 so that the motor rotates. Specifically, the arithmetic unit 5 controls the inverter 4 according to the procedure shown in the flowchart shown in FIG.

In the arithmetic unit 5, the pressure sensor 2
From the measured pressure P, the set rotation speed (N) calculated according to the equation (II) is compared with a designated rotation speed (Ns) which is a rotation speed corresponding to a control command output to the inverter 4. .

When the absolute value of the difference between the commanded rotation speed (Ns) and the set rotation speed (N) is larger than a fixed value ΔN, the arithmetic unit 5 determines based on the pressure P from the pressure sensor 2. A new set speed (N) is calculated, and the set speed (N) is compared with the designated speed (Ns).

On the other hand, when the absolute value of the difference between the designated rotational speed (Ns) and the set rotational speed (N) is smaller than a fixed value ΔN, the arithmetic unit 5 sets the set rotational speed (N) and the designated rotational speed (N). The number of rotations (Ns) is compared. When the set rotation speed (N) is lower than the designated rotation speed (Ns), the arithmetic unit 5
Outputs a higher designated rotation speed (Ns) toward the inverter 4. As a result, the rotation speed of the centrifugal pump 1 increases, and the pressure P detected by the pressure sensor 2 is increased.
As a result, the set rotation speed (N) calculated by the arithmetic unit 5 also becomes higher, and the designated rotation speed (Ns) eventually coincides with the set rotation speed (N).

On the other hand, the set number of revolutions (N) is equal to the designated number of revolutions (N
If s) is higher, the arithmetic unit 5 outputs a lower designated rotation speed (Ns) toward the inverter 4. As a result, the rotation speed of the centrifugal pump 1 decreases, so that the pressure P detected by the pressure sensor 2 also decreases. As a result, the set rotation speed (N) calculated by the arithmetic unit 5 also decreases, and the instruction is eventually given. The rotation speed (Ns) matches the set rotation speed (N).

2. 2. Configuration of Flow Control Apparatus of Present Invention 2.1 Pump Pumps used in the pump flow control apparatus of the present invention include pumps used for water supply, and specifically, centrifugal pumps, axial flow pumps, and the like. A turbo type pump such as a mixed flow pump can be used.

2.2 Pressure Sensor The pressure sensor has a function of converting the discharge pressure of the pump into a signal that can be processed by an arithmetic unit described later.

Here, the discharge pressure of the pump that can be measured by the pressure sensor includes a pressure at a discharge port of the pump and a discharge pipe pressure in a discharge pipe of the pump. Further, when a check valve is inserted in the discharge pipe, the pressure of a portion of the discharge pipe upstream of the check valve may be measured as the discharge pressure. The pressure downstream of the stop valve may be measured as the discharge pressure.

As the pressure sensor, the discharge pressure is determined by the pressure such as air pressure and hydraulic pressure, electric capacity, inductance,
An apparatus having a function of converting into various signals such as an electric signal selected from an electric resistance and a frequency of an alternating current, and transmitting the discharge pressure converted into the various signals to an arithmetic unit described later can be given. .

Accordingly, as the pressure sensor, specifically, a pneumatic converter for converting a change in discharge pressure into a change in air pressure and a hydraulic converter for converting a change in discharge pressure into a change in hydraulic pressure are used. And a converter for converting a change in discharge pressure into various electrical signals. Examples of the electric transducer include a capacitive transducer that converts a change in discharge pressure into a change in electric capacity, an inductance converter that converts a change in discharge pressure into a change in inductance of a coil, and a thin film strain gauge that changes the discharge pressure. And a strain gauge type transducer for converting a change in electric resistance in a strain gauge such as a diffusion semiconductor strain gauge, and a change in discharge pressure into a vibration of a string, a beam, a diaphragm, a cylinder, etc., and this vibration is electrically converted. And electrical converters such as vibration converters for detecting the above. Particularly preferred pressure transducers among the pressure transducers include the above-mentioned electric transducers.

2.3 Motor Examples of the motor for driving the pump include various DC motors and AC motors. Among these motors, synchronous motors and induction motors are most preferable because they are inexpensive and robust.

2.4 Motor Control Unit The motor control unit has a function of controlling the number of rotations of the motor.

As the motor control device, various control devices can be mentioned according to the type of motor used.
For example, when a DC motor is used as the motor, examples of the motor control device include an Irgna-type control device and a thyristor leonard. However, when using these control devices, it is necessary to provide a speed detector on the motor or the pump, and feed back a signal of the number of revolutions from the speed detector to the control device.

When an induction motor is used as the motor, an inverter for controlling the power supply frequency, a primary voltage control device for controlling the primary voltage, and a proportional transition by changing the secondary current are used as the motor control device. And a Cervius-type control device. However, when a primary voltage controller, a Servius controller, a Kramer controller, or the like is used among these controllers, like the thyristor leonard, a motor or a pump is provided with a speed detector, and a speed detector is provided. It is necessary to feed back the rotation speed signal from the detector to the control device.

As the motor control device, an inverter is particularly preferable because an induction motor can be controlled without feedback control and a speed range can be widened.
However, when the induction motor rotates, a slip corresponding to the load is always generated, so the actual rotation speed is smaller than the rotation speed corresponding to the frequency of the AC output generated by the inverter by the slip, that is, About 1 to 3% lower. Therefore, even when controlling the induction motor using the inverter,
By detecting the speed of the induction motor with a speed detector etc. and feeding back the detected speed to the inverter,
It is preferable to compensate for the slip.

When the synchronous motor is controlled by the inverter, the synchronous motor rotates at a rotational speed proportional to the frequency of the AC output generated by the inverter. Therefore,
In this case, it is not necessary to perform the feedback control.

Examples of the inverter include inverters of various types, such as a current control type inverter, a voltage control type inverter, and a PWM type inverter.
Further, any of a transistor inverter, an IGBT inverter, and a thyristor inverter can be used.

2.5 Arithmetic Unit In the flow control device of the present invention, the arithmetic unit includes, as described above, the maximum discharge flow rate and the maximum discharge pressure of the pump in the pipe, the minimum required discharge pressure in the pipe, and the pressure. It has a function of calculating the set rotation speed of the pump based on the discharge pressure of the pump measured by the sensor, and a function of outputting a control command to the motor control device so that the pump rotates at the set rotation speed. . As described above, the set number of revolutions is the number of revolutions of the pump necessary for the discharge pressure and the discharge flow rate of the pump to satisfy the relationship indicated by the resistance curve in the pipe.

Examples of the arithmetic device include a microcomputer and a minicomputer. These microcomputers and minicomputers
It may have a numeric keypad or a keyboard for inputting various parameters.

In the arithmetic unit, the set number of revolutions of the pump is calculated from the discharge pressure (P) measured by the pressure sensor according to the procedure described for the arithmetic unit in the flow control device shown in FIG. can do.

First, the flow path resistance coefficient in a known pipe,
The maximum discharge pressure (Pmax) of the pump is calculated from the minimum required discharge pressure (Po) when the pump is stopped and the maximum discharge flow rate (Qmax) of the pump. The maximum discharge flow rate (Qmax) and the maximum discharge pressure (P
The maximum rotation speed (Nmax) is determined from the performance curve of the pump passing through the maximum flow point (Qmax, Pmax) given by (max).

In the arithmetic unit, the flow path resistance coefficient in a known pipe, the minimum required discharge pressure (Po) when the pump is stopped, and the maximum discharge flow rate (Qmax) in the pump are determined.
In addition to the above, the values manually calculated by the operator for the maximum discharge pressure (Pmax) and the maximum rotation speed (Nmax) are also
It can be input through a numeric keypad or a keyboard. The flow resistance coefficient and the minimum required discharge pressure (Po)
And the maximum discharge flow rate (Qmax and the maximum discharge pressure (Pmax)
And a known discharge flow rate (Qset)
And the number of rotations of the pump (Nse) at the discharge pressure (Pset)
t), the maximum discharge flow rate (Qmax), and the maximum discharge pressure (P
max) and a formula for calculating the maximum number of revolutions (Nmax) is stored in an arithmetic unit, and the flow path resistance coefficient, minimum required discharge pressure (Po) and maximum From the discharge flow rate (Qmax), the maximum discharge pressure (Pmax) and the maximum rotation speed (Nmax)
May be automatically calculated.

Next, when the minimum required discharge pressure (Po) is used as the pressure during the shutoff operation of the pump, the shutoff rotation speed (No) of the pump is calculated.

With respect to the shut-off speed (No), the operator reads the value read from the performance curve of the pump when the shut-off operation is performed with the minimum required discharge pressure (Po) as the shut-off operation pressure. Can be entered.

Further, the cutoff rotation speed (No) obtained by actual measurement
Can be input to the computing device through a numeric keypad or a keyboard.

Further, using the fact that the discharge pressure of the pump is proportional to the square of the rotation speed of the pump, the cutoff pressure (Plim) at the maximum rotation speed Nmax and the minimum required discharge pressure (Po) are used to calculate the above-mentioned arithmetic unit. Relations stored internally:

[0102]

(Equation 16)

Thus, the cutoff rotational speed (No) may be calculated in the arithmetic unit.

In addition to this, a certain known discharge flow rate (Qset
), The formula for calculating the shut-off speed (No) of the pump from the pump speed (Nset) at the discharge pressure (Pset) and the minimum required discharge pressure (Po) is stored in the arithmetic unit. The minimum required discharge pressure (Po) previously input by the operator as a known parameter
Thus, the shut-off speed (No) of the pump may be automatically calculated.

Next, the arithmetic unit inputs and calculates the maximum discharge flow rate (Qmax), maximum discharge pressure (Pmax), maximum rotation speed (Nmax), minimum required The set number of revolutions (N) is calculated from the discharge pressure (Po), the shutoff speed (No), and the discharge pressure (P) measured by the pressure sensor.

From the parameters such as the maximum discharge flow rate (Qmax), the formula for calculating the set number of revolutions (N) is as follows.

[0107]

[Equation 17]

(However, ΔP = Pmax−P and ΔPo
= Pmax-Po. ) Can be used.

The above relational expression can be expressed as follows: (a) The maximum flow point (Qmax,
Pmax), a resistance curve f (Q, P) given by a quadratic curve connecting the shutoff operation point (0, Po), the maximum flow point (Qmax, Pmax), and the pump stop point (0, Po).
0), a similar operating point curve g (Q, P) which is a locus of similar operating points when the rotation speed of the pump is changed, and a similar curve at a shutoff speed (No). A surface surrounded by a closed curve having three sides of a pump performance curve ho (Q, P), the resistance curve f (Q, P), a similar operating point curve g (Q, P), and a set rotation speed. (N) that the performance curve hN (Q, P) of the pump is similar to a surface surrounded by a closed curve having three sides, and
(b) the discharge pressure and the discharge flow rate of the pump are the resistance curve f
It can be derived on the assumption that the required end pressure is obtained when changing along (Q, P).

In the pump flow control device of the present invention,
In addition to the function of calculating the set rotation speed (N) of the pump, the function of outputting a control command to the motor control device so that the pump rotates at the set rotation speed, and the use amount of water supply increases or decreases as an arithmetic device In addition, an arithmetic unit having a function of keeping the feed water pressure constant by increasing or decreasing the rotation speed of the pump can also be used. The procedure for keeping the feed water pressure constant in the arithmetic unit will be described in detail in "Another example of the pump flow control device according to the present invention" described later. 3. Operation of the present invention In the pump flow control device of the present invention, the set rotation speed (N) is calculated from the discharge pressure (P) measured by the pressure sensor in accordance with the above two preconditions.

Therefore, when the pump flow control device of the present invention is used, when the discharge pressure is P, the set rotation speed (N)
Since the pump rotates at a rotational speed substantially equal to the above, feed water is discharged from the pump at a discharge flow rate (Q) given by the resistance curve f (Q, P) and the discharge pressure (P).
Here, the minimum required discharge pressure (Po) of the water supply pipe is constant regardless of the discharge flow rate (Q), and is given by the sum of the actual head of the water supply pipe and the required terminal water supply pressure. On the other hand, the discharge pressure P is, as described above, the pressure required to overcome the flow path resistance and allow water to flow through the water supply pipe at the flow rate Q, the pressure corresponding to the actual head of the water supply pipe, and the required terminal pressure. It is given as the sum with the feedwater pressure. Therefore, when the discharge pressure is P, by rotating the pump at the set rotation speed (N), water is always supplied from the end of the water supply pipe at a predetermined water supply pressure and flow rate Q.

4. Another example of the pump flow rate control device according to the present invention In the pump flow rate control device shown in FIG. 1, the set rotation speed of the pump (P) based on the discharge pressure (P) of the pump measured by the pressure sensor based on the above relational expression. N) function to calculate,
The function of rotating the pump at the set number of revolutions (N), and when the amount of water used suddenly increases or decreases, the number of revolutions of the pump is increased or decreased according to the increase or decrease in the amount of water used to keep the water supply pressure constant. An example using an arithmetic device having a function of holding will be described below.

In the pump flow control device, the pump 1, the pressure sensor 2, the motor 3, the inverter 4, the water supply pipe 6, the check valve 61, and the on-off valve 62 are the same as those in the pump flow control device shown in FIG. Pump 1, pressure sensor 2,
It has the same structure and function as the motor 3, the inverter 4, the water supply pipe 6, the check valve 61, and the on-off valve 62. or,
Also in the arithmetic unit 5, the minimum required water supply pressure (Po)
, The maximum discharge flow rate (Qmax), the maximum discharge pressure (Pmax) of the centrifugal pump 1, the maximum rotation speed (Nmax), the cutoff rotation speed (No), and the discharge pressure (P) input from the pressure sensor 2. From the following formula (II)

[0114]

(Equation 18)

(However, ΔP = Pmax−P and ΔPo
= Pmax-Po. ), The set number of revolutions (N) is calculated.

Further, in the arithmetic unit 5, when the amount of water used suddenly increases or decreases, the terminal pressure in the water supply pipe 6 is kept constant by increasing or decreasing the rotation speed of the centrifugal pump 1 as follows.

The discharge flow rate of the centrifugal pump when the amount of water used in the pump flow control device increases,
FIG. 4 shows changes in the discharge pressure and the number of revolutions, and FIG. 5 shows changes in the discharge flow rate, the discharge pressure, and the number of revolutions of the centrifugal pump when the amount of water used decreases.

In the pump flow control device, the centrifugal pump 1 rotates at the rotation speed (Nset) by the control signal from the arithmetic unit 5, and water is supplied to the water supply pipe 6 at the discharge pressure (Pset) and the discharge flow (Qset). It is assumed that it is supplied.
A point B (Qset, Pset) in FIGS. 4 and 5 is a point corresponding to the above state.

First, the case where the amount of water used increases will be described.

When the amount of water used increases, the amount of water supplied to the water supply pipe 6 increases, so that the discharge flow rate of the centrifugal pump 1 naturally increases. Therefore, the rotation speed (Nset) shown in FIG.
As can be seen from the performance curve hN (Q, P) of the centrifugal pump 1 at
), The discharge pressure (P) is lower than the discharge pressure (Pset). Here, let the discharge pressure at the time of a fall be discharge pressure (Pa).

When the pressure sensor 2 detects that the discharge pressure (P) has decreased to the discharge pressure (Pa), the arithmetic unit 5
First, based on the equation (II), the discharge pressure (Pa)
Is calculated and compared with the rotational speed (Nset) of the centrifugal pump 1 at the point B (Qset, Pset). When the rotation speed (N1 is lower than the rotation speed (Nset),
Determines that the discharge pressure (Pa) is too low, and outputs a control command to the inverter 4 so that the designated rotational speed (Ns) becomes higher than the rotational speed (N1).

On the other hand, the arithmetic unit 5 calculates the performance curve H
Based on N (Q, P), the centrifugal pump 1
), The discharge flow rate (Qa) corresponding to the discharge pressure (Pa) is estimated. The arithmetic unit 5 includes:
Further, based on the resistance curve f (Q, P), the required end pressure (Hp) at the discharge flow rate (Qa) in the water supply pipe 6 is obtained.
The discharge pressure (Pa ') required to obtain the following is estimated. The pressure detected by the pressure sensor 2 is equal to the estimated discharge pressure (P
When it becomes equal to a '), a control command is output to the inverter 4 to set the rotation speed (N2) at this time to the designated rotation speed (Ns). Therefore, the centrifugal pump 1 rotates at the rotation speed (N2). The discharge flow rate of the centrifugal pump 1 at this time is naturally (Qa), and the point given by the discharge flow rate (Qa) and the discharge pressure (Pa ') is on the resistance curve f (Q, P). Located in. Therefore, the water supply pipe 6
Is a predetermined terminal pressure (Hp).
In FIG. 4, a performance curve hN2 (Q, P) indicates a performance curve when the centrifugal pump 1 rotates at the rotation speed N2.

Next, the case where the amount of water used is reduced will be described.

When the amount of water supply decreases, the amount of water supplied to the water supply pipe 6 decreases, so that the discharge flow rate of the centrifugal pump 1 naturally decreases. Therefore, the rotation speed (Nset) shown in FIG.
As can be seen from the performance curve hN (Q, P) of the centrifugal pump 1 at
), The discharge pressure (P) is higher than the discharge pressure (Pset). Here, the discharge pressure at the time of rising is defined as a discharge pressure (Pb).

When the pressure sensor 2 detects that the discharge pressure (P) has increased to the discharge pressure (Pb), the arithmetic unit 5
First, based on the formula (II), the discharge pressure (Pb)
Is calculated and compared with the rotation speed (Nset) of the centrifugal pump 1 at the point B (Qset, Pset). If the rotation speed (N3 is higher than the rotation speed (Nset), the arithmetic unit 5
Determines that the discharge pressure (Pb) is too low, and outputs a control command to the inverter 4 so that the designated rotational speed (Ns) becomes lower than the rotational speed (N3).

On the other hand, the arithmetic unit 5 calculates the performance curve H
Based on N (Q, P), the centrifugal pump 1
), The discharge flow rate (Qb) corresponding to the discharge pressure (Pb) is estimated. The arithmetic unit 5 includes:
Further, based on the resistance curve f (Q, P), the required terminal pressure (Hp) at the discharge flow rate (Qb) in the water supply pipe 6 is obtained.
Of the discharge pressure (Pb ') necessary to obtain the following formula. When the pressure detected by the pressure sensor 2 becomes equal to the estimated value (Pb '), a control command for setting the rotation speed (N4) at this time to the designated rotation speed (Ns) is output to the inverter 4. Therefore, the centrifugal pump 1 rotates at the rotation speed (N4). The discharge flow rate of the centrifugal pump 1 at this time is (Qb), and the point given by the discharge flow rate (Qb) and the discharge pressure (Pb ') is the resistance curve f
(Q, P). Therefore, the terminal pressure in the water supply pipe 6 becomes a predetermined terminal pressure (Hp). FIG.
HN4 (Q, P) indicates the performance curve of the centrifugal pump 1 at the rotation speed (N4).

In the pump flow control device, when the centrifugal pump 1 is rotating at the rotation speed (Nset), the amount of water used increases when the amount of water supplied increases and decreases when the amount decreases. In this case, the terminal pressure in the water supply pipe 6 can be maintained at a constant value by increasing or decreasing the rotation speed of the centrifugal pump 1.
When the amount of water used suddenly increases, the terminal pressure becomes too low to supply water sufficiently, and when the amount of water used suddenly decreases, water suddenly flows out of the faucet. Are prevented.

[0128]

According to the present invention, it is necessary to store a large number of pressures determined at the intersection between the performance curve and the resistance curve of the water supply line for each operation speed at the intersection along the resistance curve of the water supply line. There is no need for a large amount of memory,
Further, a pump flow control device which can easily perform continuous control and further contributes to significant energy saving is provided.

Among the pump flow control devices provided by the present invention, the pump flow control device provided with an arithmetic unit having a function of increasing or decreasing the rotation of the centrifugal pump 1 in accordance with an increase or decrease in the amount of water used has the above-mentioned features. In addition, there is a feature that the feed water pressure is kept substantially constant even when the amount of feed water used changes rapidly.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a configuration of a pump flow control device of the present invention.

FIG. 2 shows a maximum flow point A (Qmax, Pmax), a point B (Q, P), a point C (Q ′, P ′), and a shutoff operation point D.
(0, Po), point E (Q1, P1), pump stop point O (0, 0), resistance curve f (Q, P) and similar operating point curve g (Q, P) in piping, and performance Curve hmax
(Q, P), performance curve ho (Q, P), and performance curve h
It is a schematic diagram showing a relation with N (Q, P).

FIG. 3 is a flowchart showing a procedure in which the arithmetic unit 5 controls the inverter 4 in the pump flow control device shown in FIG.

FIG. 4 is a graph showing changes in the discharge flow rate, the discharge pressure, and the number of revolutions of the centrifugal pump when the amount of water used increases.

FIG. 5 is a graph showing changes in the discharge flow rate, the discharge pressure, and the number of revolutions of the centrifugal pump when the amount of water used decreases.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Pump, 2 ... Pressure sensor, 3 ... Motor, 4 ... Inverter, 5 ... Calculation device, 6 ...
Water supply pipe, 61 ... check valve, 62 ... open / close valve, 7.
..Speed detectors.

Claims (2)

[Claims] A pump connected to a known pipe, a pressure sensor for measuring a discharge pressure of the pump, a motor for driving the pump, a motor control device for controlling a rotation speed of the motor, and the pipe Based on the maximum discharge flow rate and the maximum discharge pressure of the pump, the minimum required discharge pressure in the piping, and the discharge pressure of the pump measured by the pressure sensor, calculate the set rotation speed of the pump corresponding to the discharge pressure And a computing device that outputs a control command to the motor control device so that the pump rotates at the set number of revolutions. 2. The arithmetic unit according to claim 1, wherein (A) the flow resistance coefficient, the minimum required discharge pressure (Po), and the maximum discharge flow rate (Qmax) in the known pipe
The maximum discharge pressure (Pmax) of the pump is determined, and the maximum discharge flow rate (Qmax) and the maximum discharge pressure (Pma) of the pump are determined.
x) and the maximum speed (Nmax) corresponding to the performance curve of the pump passing through the maximum flow point (Qmax, Pmax) given by
And (B) the minimum required discharge pressure (Po) as a shutoff operating pressure, which passes through a shutoff operating point (0, Po) given by the shutoff operating pressure (Po) and the flow rate Q being 0. (C) (a) the maximum flow point (Q)
max, Pmax) and the resistance curve f (Q, P) in the pipe, given by a quadratic curve connecting the shutoff operating point (0, Po), and the maximum flow point (Qmax, Pmax).
) And a quadratic curve passing through the pump stop point (0, 0), a similar operating point curve g (Q, P) which is a locus of similar operating points when the rotation speed of the pump is changed, The performance curve ho of the pump at the shut-off speed (No)
(B) a surface surrounded by a closed curve having (Q, P) as three sides, (b) the resistance curve f (Q, P), and a similar operating point curve g
The pressure defined in claim 1, wherein a surface surrounded by a closed curve having three sides of (Q, P) and a performance curve hN (Q, P) of the pump at a set rotation speed (N) is similar to each other. The pump flow rate control device according to claim 1, wherein the set rotation speed (N) of the pump according to claim 1 is calculated according to a procedure of calculating a set rotation speed (N) at a pressure P measured by a sensor.